Apache Derby Database Engine and Embedded JDBC Driver 10.17.1.0 · org.apache.derby.impl.services.cache.BackgroundCleaner

A background cleaner that ConcurrentCache can use to clean Cacheables asynchronously in a background instead of synchronously in the user threads. It is normally used by the replacement algorithm in order to make dirty Cacheables clean and evictable in the future. When the background cleaner is asked to clean an item, it puts the item in a queue and requests to be serviced by a DaemonService running in a separate thread.

Field Summary

Modifier and Type	Field and Description
private final ConcurrentCache	cacheManager The cache manager owning this cleaner.
private final int	clientNumber Subscription number for this `Serviceable`.
private final DaemonService	daemonService The service thread which performs the clean operations.
private final ArrayBlockingQueue<CacheEntry>	queue A queue of cache entries that need to be cleaned.
private final AtomicBoolean	scheduled Flag which tells whether the cleaner has a still unprocessed job scheduled with the daemon service.
private volatile boolean	shrink Flag which tells whether the cleaner should try to shrink the cache the next time it wakes up.

Constructor Summary

Access	Constructor and Description
pack-priv	BackgroundCleaner(ConcurrentCache the cache manager that owns the cleaner cache, DaemonService the daemon service which perfoms the work daemon, int the maximum number of entries to keep in the queue (must be greater than 0) queueSize) Create a background cleaner instance and subscribe it to a daemon service.

Method Summary

Modifier and Type	Method and Description
public int	Returns: status for the performed work (normally `Serviceable.DONE`) performWork(ContextManager ignored context) Implements org.apache.derby.iapi.services.daemon.Serviceable.performWork. Clean the first entry in the queue.
private void	requestService() Notify the daemon service that the cleaner needs to be serviced.
pack-priv boolean	Returns: `true` if the entry has been scheduled for clean, `false` if the background cleaner can't clean the entry (its queue is full) scheduleClean(CacheEntry the entry that needs to be cleaned entry) Try to schedule a clean operation in the background cleaner.
pack-priv void	scheduleShrink() Request that the cleaner tries to shrink the cache the next time it wakes up.
public boolean	Returns: `true` serviceASAP() Implements org.apache.derby.iapi.services.daemon.Serviceable.serviceASAP. Indicate that we want to be serviced ASAP.
public boolean	Returns: `false` serviceImmediately() Implements org.apache.derby.iapi.services.daemon.Serviceable.serviceImmediately. Indicate that we don't want the work to happen immediately in the user thread.
pack-priv void	unsubscribe() Stop subscribing to the daemon service.

Inherited from java.lang.Object:: clone equals finalize getClass hashCode notify notifyAll toString wait wait wait

Field Detail

cacheManager	back to summary
private final ConcurrentCache cacheManager The cache manager owning this cleaner.

clientNumber	back to summary
private final int clientNumber Subscription number for this `Serviceable`.

daemonService	back to summary
private final DaemonService daemonService The service thread which performs the clean operations.

queue	back to summary
private final ArrayBlockingQueue<CacheEntry> queue A queue of cache entries that need to be cleaned.

scheduled	back to summary
private final AtomicBoolean scheduled Flag which tells whether the cleaner has a still unprocessed job scheduled with the daemon service. If this flag is `true`, calls to `serviceNow()` won't result in the cleaner being serviced.

shrink	back to summary
private volatile boolean shrink Flag which tells whether the cleaner should try to shrink the cache the next time it wakes up.

Constructor Detail

BackgroundCleaner	back to summary
pack-priv BackgroundCleaner(ConcurrentCache cache, DaemonService daemon, int queueSize) Create a background cleaner instance and subscribe it to a daemon service. Parameters cache:ConcurrentCache the cache manager that owns the cleaner daemon:DaemonService the daemon service which perfoms the work queueSize:int the maximum number of entries to keep in the queue (must be greater than 0)

BackgroundCleaner

back to summary

pack-priv BackgroundCleaner(ConcurrentCache cache, DaemonService daemon, int queueSize)

Create a background cleaner instance and subscribe it to a daemon service.

Parameters

cache:ConcurrentCache: the cache manager that owns the cleaner
daemon:DaemonService: the daemon service which perfoms the work
queueSize:int: the maximum number of entries to keep in the queue (must be greater than 0)

Method Detail

performWork back to summary

performWork	back to summary
public int performWork(ContextManager context) throws StandardException Implements org.apache.derby.iapi.services.daemon.Serviceable.performWork. Clean the first entry in the queue. If there is more work, re-request service from the daemon service. Parameters context:ContextManager ignored Returns:int status for the performed work (normally `Serviceable.DONE`) Exceptions StandardException: if `Cacheable.clean()` fails

public int performWork(ContextManager context) throws StandardException

Implements org.apache.derby.iapi.services.daemon.Serviceable.performWork.

Clean the first entry in the queue. If there is more work, re-request service from the daemon service.

Parameters

context:ContextManager: ignored

Returns:int

status for the performed work (normally Serviceable.DONE)

Exceptions

StandardException:: if Cacheable.clean() fails

requestService	back to summary
private void requestService() Notify the daemon service that the cleaner needs to be serviced.

scheduleClean back to summary

scheduleClean	back to summary
pack-priv boolean scheduleClean(CacheEntry entry) Try to schedule a clean operation in the background cleaner. Parameters entry:CacheEntry the entry that needs to be cleaned Returns:boolean `true` if the entry has been scheduled for clean, `false` if the background cleaner can't clean the entry (its queue is full)

pack-priv boolean scheduleClean(CacheEntry entry)

Try to schedule a clean operation in the background cleaner.

Parameters

entry:CacheEntry: the entry that needs to be cleaned

Returns:boolean

true if the entry has been scheduled for clean, false if the background cleaner can't clean the entry (its queue is full)

scheduleShrink	back to summary
pack-priv void scheduleShrink() Request that the cleaner tries to shrink the cache the next time it wakes up.

serviceASAP back to summary

serviceASAP	back to summary
public boolean serviceASAP() Implements org.apache.derby.iapi.services.daemon.Serviceable.serviceASAP. Indicate that we want to be serviced ASAP. Returns:boolean `true`

public boolean serviceASAP()

Implements org.apache.derby.iapi.services.daemon.Serviceable.serviceASAP.

Indicate that we want to be serviced ASAP.

Returns:boolean: true

serviceImmediately back to summary

serviceImmediately	back to summary
public boolean serviceImmediately() Implements org.apache.derby.iapi.services.daemon.Serviceable.serviceImmediately. Indicate that we don't want the work to happen immediately in the user thread. Returns:boolean `false`

public boolean serviceImmediately()

Implements org.apache.derby.iapi.services.daemon.Serviceable.serviceImmediately.

Indicate that we don't want the work to happen immediately in the user thread.

Returns:boolean: false

unsubscribe	back to summary
pack-priv void unsubscribe() Stop subscribing to the daemon service.

pack-priv final Class BackgroundCleaner

Field Summary

Constructor Summary

Method Summary

Field Detail

Constructor Detail

Method Detail